Criteria for ischemic changes in the esophageal electrocardiograph (E-ECG) have not been standardized and validated. The main goal of this study was to evaluate the experimental esophageal recording of myocardial ischemia and to assess the association between ST segment alternans in the E-ECG and ischemia. Experiments were performed on 18 anesthetized sheep with occlusion of a branch of the left anterior descending artery. The bipolar signals were recorded via an esophageal lead containing three chloridized silver electrodes. Electrical signals were amplified in a self-designed, battery-supported preamplifier (gain 1000, frequency range 0.01-2000 Hz, common mode rejection 140 dB, signal noise 5-7 microV p-p), then sent to a digital oscilloscope for display and to a pulse code-modulated recorder. Surface electrocardiography (S-ECG) data were also recorded. Ischemia E-ECG revealed homogenous ST segments without any beat-to-beat alternans. Two minutes after occlusion, 14 of 15 sheep (93%) showed repetitive beat-to-beat fluctuations within the ST segment on the E-ECG. Of the 15 sheep, 7 (47%) showed ischemia in the S-ECG (P < 0.01). For calculation of the dynamic changes in the ST segment in the E-ECG, the difference in the amplitudes of the ST segment of five successive beats to the next beat, performed for 200 consecutive beats, was calculated. The central tendency of the sum of these values before versus during ischemia was 2000 mV/ms versus 5000 mV/ms (Hodges-Lehmann point estimator) (95% confidence intervals 1700/2500 versus 3350/9250 [lower limit/upper limit]). The authors have established a close temporal relationship between the magnitude of ST segment alternans recorded via E-ECG and myocardial ischemia.
Implications: The study presents the use of an esophageal electrocardiograph for detection of progressive changes of myocardial ischemia and infarction. During acute myocardial ischemia and infarction in sheep, the esophageal electrocardiograph has visually apparent ST alternans of amplitude in the millivolt range, in part due to a special amplifier (0.01-2000 Hz). This is therefore one very promising technique for better evaluation of electrocardiographic changes of ischemia.